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1999 GMC sierra oil pressure guage reads erratic


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#1 xm22rx

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Posted 18 February 2012 - 12:30 AM

Hi i own a 1999 gmc sierra with a 5.3l and automatic trans the truck has 199,000 miles and ive had no mechanical issues with it the whole life of the truck. There is one thing that does concern me approximately 50,000 miles ago the oil pressure guage started reading eratic at first it would just vibrate rapidly around its normal range it did that for awhile but now in the last 10,000 miles its still doing the rapid bouncing but now at idle it dips down to the 40 mark on the guage until the rpms are brought up then it comes up on the pressure reading. IIve heard that these engines had weak oil pumps? I dont know if thats true or not. Does this sound like a bad pump or guage or? Thanks for you time.

#2 Jsdirt

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Posted 18 February 2012 - 06:02 AM

199K & no issues? Well you'd better keep it! Stay away from the new ones. I've got 52k and lots of issues ...

But anyway - lots of the time the gauges (stepper motors), or the sender goes bad. Back in the day that was a GM trait on high mileage vehicles - the bouncy oil pressure gauge. Nowadays with all the shoddy components they use, you can't be 100% sure without testing. If your concerned with the oil pump I'd get a real gauge & hook it up to the block for a true reading - only then can you rule out the oil pump.
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#3 GMstrong

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Posted 18 February 2012 - 07:15 AM

These truck have bad oil pumps?Thats a first.Its your cluster mine does the same thing.As long as the oil pressure doesnt go below psi then i wouldnt worry.Some people say dont let it go below 10-15psi but i wouldnt let my trucks run without more then 20psi.
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#4 oldscsc

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Posted 18 February 2012 - 10:38 AM

Mine does this also. My gauge started reading quite a bit less all of a sudden, and erratically (sometimes you can watch the needle dance). Since the 99-02 stepper motors are usually trouble free I've always assumed it's the sending unit; it sure doesn't look like much fun to get to though.
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#5 brandylachacha

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Posted 23 November 2015 - 10:31 PM

i have a 99 gmc sierra. start it up, zero pressure. builds up to just over 40. as it warms up (also rev it up) it drops to zero. changed oil pressure sending unit. same problem. any ideas? that dont involve getting the pump out?


Edited by brandylachacha, 23 November 2015 - 10:45 PM.


#6 amc31b

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Posted 23 November 2015 - 11:43 PM

This post may help.....

 

 

http://www.gm-trucks...ressure-issues/


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#7 00Silverado4x4

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Posted 24 November 2015 - 10:10 AM

i have a 99 gmc sierra. start it up, zero pressure. builds up to just over 40. as it warms up (also rev it up) it drops to zero. changed oil pressure sending unit. same problem. any ideas? that dont involve getting the pump out?

Verify the oil pressure with a mechanical gauge.  If still at 0 or slow to build up, you're looking at a pump/pick up tube issue.


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#8 brandylachacha

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Posted 24 November 2015 - 10:22 AM

Yeah I have the mechanical gauge to put on it. But it's such a pain to get to. Have to get creative I guess -_-




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